[UNOMI-Test] - Add test for DataTable$Row.toString and DataTable.toString

Hey 😊 I want to contribute a test. Curious to hear what you think!

(I wrote this test as part of a research study at TU Delft. Find out more)

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Please following this checklist to help us incorporate your contribution quickly and easily:

• [x] Make sure there is a JIRA issue filed for the change (usually before you start working on it). Trivial changes like typos do not require a JIRA issue. Your pull request should address just this issue, without pulling in other changes. -> I believe this to count as a trivial change
• [x] Format the pull request title like [UNOMI-XXX] - Title of the pull request
• [x] Provide integration tests for your changes, especially if you are changing the behavior of existing code or adding significant new parts of code. -> no new code, but providing tests 🙂
• [x] Write a pull request description that is detailed enough to understand what the pull request does, how, and why. Copy the description to the related JIRA issue
• [x] Run mvn clean install -P integration-tests to make sure basic checks pass. A more thorough check will be performed on your pull request automatically. -> passes

Trivial changes like typos do not require a JIRA issue (javadoc, project build changes, small doc changes, comments...).

If this is your first contribution, you have to read the Contribution Guidelines -> leads me to a 404 unfortunately :/ I have read the general contribution guidelines in other apache repositories.

• [x] I hereby declare this contribution to be licenced under the Apache License Version 2.0, January 2004

Hello,

Thank you for your contribution. We require that pull requests are associated with a ticket in Unomi's JIRA. Could you please either create a ticket there or associate it to an existing one (if you can find a relevant one). You can find the Unomi JIRA here: https://issues.apache.org/jira/projects/UNOMI/summary

Best regards, Serge Huber.

Also, once you have created a ticket, please update the title of the PR to include the ticket number in the title. Thank you.

Unfortunately I can't access the JIRA under the link you gave me or the one from the issue template :/ The page just keeps loading & ends in a 'server took to long to respond' on both my Firefox and Chrome. What is the trick to access it? 🙂

My issue would be very similar to the title of this PR: Add a test case for DataTable$Row.toString and DataTable.toString, which are as far as I see not covered by another test yet.

Ok I've created the JIRA ticket : https://issues.apache.org/jira/browse/UNOMI-645 and merge your changes ! Thanks again for your contribution.